D y n a m a r. The Effects of Processing Aids on the Hot-Tack Properties of LLDPE Blown Films. Polymer Processing Additives

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1 D y n a m a r Polymer Processing Additives No. 21 The Effects of Processing Aids on the Hot-Tack Properties of LLDPE Blown Films Jim H. Addcox Senior Technical Service Engineer Chevron Chemical LLC Glen M. Giacoletto Senior Chemical Engineer Dyneon LLC

2 The Effects of Processing Aids on the Hot-Tack Properties of LLDPE Blown Films ABSTRACT Fluorine-based processing aids are an effective means for improving the surface quality of polymer extrudates, especially in LLDPE film applications. By reducing the shear induced stresses which can cause melt fracture and die-lip build-up, processing aids have also allowed many film processors to increase the output of their equipment. Although their effects on extrusion processes are generally viewed as positive, the effects of processing aids on downstream film properties have been a historical concern. Many studies have been conducted which indicate that most commercially available processing aids have little or no effect on surface related film properties such as print adhesion and heat-seal integrity. In terms of heat-seal, these studies have focused primarily on the effects of fully quenched seals. In high-speed filling operations, such as vertical form and fill loading, the film processor must often rely on the hot-tack strength of the film to bear the weight of the load until the seal has fully quenched. In this study, three different fluorine-based processing aids were evaluated in a monolayer LLDPE film application over a range of concentrations. The hot-tack performance of these films was not adversely affected by the processing aids. INTRODUCTION Fractional melt index LLDPE film resins are often used in high strength bag applications. Because of the relatively high melt viscosity of these resins, film producers often depend on fluorine-based processing aids to improve processability and film quality. Downstream conversion of these films can often include high speed bag-filling operations which depend on the hot-tack strength of the film to support the bags content until the heat-seals have fully quenched. It is important that fluorine-based processing aids do not adversely affect the hot-tack strength of these films. EXPERIMENTAL Resin & Film Sample Preparation Three different types of fluorine-based processing aids were selected for this study. These processing aids were supplied by Dyneon LLC and are shown in Table I. Table I. Processing Aids Code PPA-1 PPA-2 PPA-3 Commercial Name Dynamar FX-9613 Dynamar FX-5920A Dynamar FX-5911X Each of these processing aids was compounded into a 1- hexene LLDPE film resin with a melt index of 0.50 g/10 min. and a density of g/cc. This base resin was produced on a British Petroleum gas phase technology reactor. The samples were prepared through the neat addition of the processing aid using a 58 min twin-screw compounding extruder with an underwater die-face pelletizer. Other than a standard film grade antioxidant package, no other additives were incorporated into the resin. For each type of processing aid studied, three concentrations were compounded into the base resin. A blank base resin sample containing no processing aid was also compounded for use as a control. The concentration of processing aid in the compounded resins was confirmed using a Parr bomb technique and ion specific electrode to measure the total fluorine content. Microscopic analysis of the compounded resins verified that the processing aids were adequately dispersed in the resin. A full description of the resins can be found in Table II. The resins were converted into films using a 63.5 min extruder fitted with a 20.3 cm diameter blown film die with a 2.54 min die gap. To insure that each film sample in the study had similar surface qualities, the samples were extruded at a relatively low shear rate. The film fabrication output for each sample was maintained at a nominal 1.07 kg/hr/cm of die circumference and the film thickness was targeted at 50.8 µm. The films were allowed to age one week prior to testing. 1

3 Test Specimen Preparation & Experimental Design Test specimens were prepared by cutting 25.4 min wide strips oriented in the machine direction (MD) so that the hot tack seal was perpendicular to the film orientation. The hot tack strength of duplicate specimens was tested using a J&B (formerly Top Wave) hot tack tester. The specific instrument settings for testing the specimens are listed in the Table III. A modified 2 factor, 3 level factorial design of experiment was selected for this study. The order in which the samples were tested was randomized and blanks were analyzed at the beginning, middle, and end of the series to monitor for possible shifts in test response. RESULTS AND DISCUSSION The average peel strength for each processing aid level is reported in Table IV. Also included in Table IV is the pooled average peel strength for each resin across all levels of processing aid at each temperature. Plots of the hot tack peel strength curves are shown in Figures I & 2. Model The data was analyzed using an analysis of variance (ANOVA) allowing for eleven levels of temperature. The level of processing aid and the replicate runs were included as factors in the ANOVA. The model is where: Yijk is the observation. Yijk = Ti + Aj TAij +Rjk + εijk Ti is the seal temperature, C (75 to 125 at 5 increments). This factor is fixed. Aj is the additive level: low, middle, high. This factor is fixed. TAij is the temperature by additive level interaction. Rjk is the replicate run within each additive level: I and 2. This factor is random. none of these factors had practical significance. This is further illustrated in the pooled data in Figure 3. The hot tack average peak value for the three types of processing aids is not significantly different over the concentration range studied. The maximum peel strength is approximately N for all three processing aids. Ranging from C, the temperature at which the maximum peel strength is achieved is also not significantly different. These results are summarized in Table VII. There are no clear trends associated with the type or concentration of the three processing aids studied. In other words, the general hot tack curve profile, or rate at which the maximum peel strength is achieved, is similar for the types and levels of processing aid. These results are summarized in Table VIII. The major source of variability for hot tack was the individual analysis, which had a 95% confidence half-interval of ± 0.31 N. CONCLUSION For the types and concentrations of processing aid considered in this study, there appears to be no negative effect on the hot tack performance of the LLDPE films. Within the scope of this study, converting operations which depend on the hot tack performance of high strength LLDPE films should not be adversely affected by processing aids. REFERENCES 1. A. Valenza and F.P. LaManita, Intern. Polymer Processing, Extrusion Characteristics of Lubricated Linear Low Density Polyethylene, p 220 (1988). 2. A. Rudin, A. T. Worm, and J. E. Blalock, J. Plastic Film & Sheeting, Fluorocarbon Elastomer Processing Aid in Film Extrusion of Linear Low Density Polyethylenes, p 189 (1985). 3. T. J. Blong and D. Duchesne, SPE PM& D Div. Newsletter, Effects of Anti-Block/Processing Aid Combinations on LLDPE Blown Film Extrusion", vol. VII, No 1 (1989). εijk is the random variability of an observation. Summary and Interpretation The data for the ANOVA can be found in Tables V & VI in the appendix. As expected, temperature had the most influence on the hot tack peel strength of the samples. Temperature accounts for 93% - 98% of the variability as measured by the sum of squares about the mean. (R-sq Temp). Although some of the other factors in the model appeared to be statistically significant, such as the temperature / processing aid level interaction, it can be argued that 2

4 Table II. Experimental Design Sample Code Processing Aid Target Experimental Concentration, ppm Concentration, ppm ER2343 Blank ER2344 PPA-1 Low ER2345 PPA-1 Middle ER2346 PPA-1 High ER2347 PPA-2 Low ER2348 PPA-2 Middle ER2349 PPA-2 High ER2350 PPA-3 Low ER2351 PPA-3 Middle ER2352 PPA-3 High Table III. Hot-Tack Instrument Variable Settings Variable Setting Description Temperature, C , 5 degree increments Seal jaw temperature setting. Dwell, sec. 0.5 Length of time seal jaws are in contact with the film. Pressure, kpa Seal jaw pressure when in contact with the film. Speed, mm/sec 200 Speed of seal separation. Delay, sec 0.5 Time lag between when the seal is made and the seal separation begins 3

5 Table IV. Average Peel Strength by Processing Aid Level Processing Seal Temperature C Aid Level N Average Peel Strength, N PPA-1 Low PPA-1 Mid PPA-1 High PPA-1 Average PPA-2 Low PPA-2 Mid PPA-2 High PPA-2 Average PPA-3 Low PPA-3 Mid PPA-3 High PPA-3 Average Blank Low Blank Mid Blank Last Blank Average

6 Table V: Analysis of Variance Analysis of Variance for FX-9613 Source DF SS MS F P SIG VC PCT VC Temp *** Add. level Level* Temp ** Rep w/i Level % Observation % Total % s(resid)=.17 R-sq (Temp) 97.3% Analysis of Variance for FX-5920A Source DF SS MS F P SIG VC PCT VC Temp *** Add. level (*) Level* Temp *** Rep w/i Level % Observation % Total % s(resid)=.15 R-sq (Temp) 93.0% Analysis of Variance for FX-5911X Source DF SS MS F P SIG VC PCT VC Temp *** Add. level * Level* Temp ** Rep w/i Level % Observation % Total % s(resid)=.16 R-sq (Temp) 96.6% Analysis of Variance for Blanks Source DF SS MS F P SIG VC PCT VC Temp *** Block * Level* Temp Rep w/i Block % Observation % Total % s(resid)=.14 R-sq (Temp) 97.7% 5

7 Table VI: Replicate Run Averages Processing Aid Level Run N FX-9613 FX-5920A FX-5911X Blank Block Low First Low First Low Pool First Low DIff First Mid Middle Mid Middle Mid Pool Middle Mid Diff Middle High Last High Last High Pool Last High Diff Last Table VII. Peak Peel Strength Comparisons Processing Aid Temperature, C Maximum Peel Strength, N 95% Confidence Interval (Pooled for all levels) (Pooled) PPA ±0.13 PPA ±0.13 PPA ±0.13 Blank ±0.13 Table VIII. Average Peel Strength Based on Processing Aid Level Processing Aid Average Peel Strength, N 95% Confidence Low Level Middle Level High Level Interval (Pooled) PPA * ±0.07 PPA * ±0.07 PPA * 2.63 ±0.07 Blank First Middle Last * ±0.07 *Denotes maximum values. 6

8 Figure 1. Individual Hot Tack Curves for PPA-1 & PPA-2 7

9 Figure 2. Individual Hot Tack Curves for PPA-3 & Blanks 8

10 Figure 3. Pooled Hot Tack Curves 9

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15 Technical Information and Test Data Technical information, test data, and advice provided by Dyneon personnel are based on inform a- tion and tests we believe are reliable and are intended for persons with knowledge and technical skills sufficient to analyze test types and conditions, and to handle and use raw polymers and re l a t- ed compounding ingredients. No license under any Dyneon or third party intellectual rights is granted or implied by virtue of this inform a t i o n. Important Notice: Because conditions of product use are outside Dyneon s control and vary widely, user must evaluate and determine whether a Dyneon product will be suitable for user s intended application before using it. T h e following is made in lieu of all expre s s and implied warranties (including warr a n t i e s of merchantability and fitness for a part i c u l a r purpose): If a Dyneon p roduct is proved to be defective, Dyneon s only obligation, and user s only re m e d y, will be, at D y n e o n s option, to replace the quantity of pro d- uct shown to be defective when user received it or to refund user s purc h a s e price. In no event will Dyneon be liable for any direct, i n d i re c t, special, incidental, or consequential loss or damage, re g a rdless of legal theory, such as b reach of w a rranty or contract, negligence, or strict liability. Dyneon 2000 Issued: 1/99, 10/00 Printed in USA All Rights Reserved Dyneon LLC rd Street North Oakdale, MN Phone: Fax: Product Information: Dyneon and Dynamar are trademarks of Dyneon This paper was prepared for presentation at TAPPI 98. Published in the 1998 TAPPI Polymers, Laminations and Coatings Conference Proceedings.